Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Low cost and high quality of the output, combined with relatively noise-free operation, have made ink-jet printers a popular alternative to other types of printers used with computers. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.
There are two basic means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through nozzles associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.
Ink-jet printers offer low cost, high quality printing with relatively noise-free operation. As such, ink-jet printers have become a popular alternative to other types of printers. Notwithstanding their recent success, intensive research and development efforts continue toward improving waterfastness, optical density, print quality, and bleed alleviation of ink-jet images. In general, waterfastness, bleed performance, and optical density of ink-jet images still falls short of that produced by other technologies such as electrophotography or gravure printing. A continued demand in ink-jet printing has resulted in the need to develop reliable printers capable of producing high quality waterfast images at a reasonable cost.
However, few ink compositions are known that possess all the foregoing desired properties, since an improvement in one property often results in the degradation of another property. Thus, many inks commercially used represent a compromise in an attempt to achieve an ink evidencing at least an adequate response in each of the performance attributes, such as waterfastness and optical density.